A good log file format can improve the quality and usefulness of logs, ensuring that the data can be easily searched, filtered, and analyzed.
It can also help you avoid common errors that can cause problems with a log management system.
There are many standard log file formats that are used in a wide variety of systems and devices. It’s important to understand how they work and how they differ from one another, so you can use them correctly.
Common Log Format (NCSA)
Log files are a common source of information for system administrators. They contain details about system errors, security incidents, and user logins. They are also useful for monitoring applications and providing insight into the performance of systems.
There are several types of log formats, and the best one depends on the specific data that you need to record. These include structured and unstructured logs.
Structured logs use a predefined schema to store data. They are typically more robust and searchable than non-structured formats.
They also require less disk space because they use a fixed number of bytes to represent each key-value pair. This is helpful if you need to store large amounts of data.
These types of logs are often used in applications that generate many log entries, such as web servers and firewalls. They are useful for troubleshooting problems with the application and are generally faster than other log formats.
Another common type of log format is the Common Log Format (NCSA). This log format is used by most Apache(tm) and Microsoft(r) Internet Information Services(r) web servers to write server logs.
The NCSA log format contains a list of fields that describe the HTTP server and the HTTP transaction. Each line in the log file contains one of these fields.
While the NCSA format can be beneficial in some situations, it can also cause problems. For example, it can make parsing the log difficult because it doesn’t use a defined pattern. This makes it hard to split events and extract key-value pairs.
Additionally, the NCSA format doesn’t support a custom file name. This can result in problems when sending the log file to a logging or SIEM system.
Moreover, the NCSA format may not be compatible with certain log analysis software. This can result in delays and unnecessary re-writing of the log file.
In some cases, you can choose to use the NCSA extended log format, which is a W3C working draft that contains additional fields that can be useful in understanding what’s happening. For instance, you can add a referral field that links a request to a client IP address. You can also add a user agent field that identifies the user of a client.
Extended Log Format (ELF)
The Extended Log Format (ELF) is a flexible format for recording HTTP requests. This format was designed by the W3C to address the limitations identified with the common log file format. It records more information than the common log format, and it allows the use of multiple headers to structure the data within a file.
This format also provides flexibility for logging tools to record different information types and is supported by most web servers. It is particularly useful for capturing data about web server errors.
In this log format, each line contains ASCII characters that are delimited by a new line. These lines can contain comment directives and fields that indicate the HTTP request fields that are actually written in the log records that follow.
ELF files can contain a program header that lists the segments used at run time, and a section header that lists the set of sections. The program header is 52 or 64 bytes long for 32-bit or 64-bit executables, respectively.
The ELF header is also used to define whether the file is being written with 32-bit or 64-bit addresses. The first three fields of the header are affected by this setting, and all fields that follow them must be interpreted accordingly.
Depending on the target architecture, these fields may be interpreted as little-endian or big-endian values. They are typically 0x7F and 0x04 for 32- or 64-bit versions of the ELF format, respectively.
These fields are normally followed by an address of the entry point in memory for a process that is using a program. This field is either 32 or 64 bits long, and it may hold zero if the program does not have an associated entry point.
The entry point is the memory location from which the application starts executing. This field is usually a fixed value, but may be an unsigned 32- or 64-bit number for statically linked executables on x86 and ARM.
In addition to the standard log file format, many semi-structured logging standards are available that allow for greater flexibility in what data is captured and how it is structured. These standards have been created to help analysts interpret and understand a broad range of log messages while providing cohesiveness across systems. These standards include Common Log Format, Extended Log Format and W3C Extended Log Format.
JSON
JSON is the most popular and widely supported data exchange format. It is a human-readable format and a standardized representation of structured data. It is also easy to parse, and can be consumed by most programming languages and operating systems right out of the box.
Originally created in the early 2000s, JSON has become a standard format for data exchange over the internet. It is a less verbose version of XML and is more suitable for web applications, which often need data to be sent in a short amount of time.
As the name suggests, JSON combines the object and array structures to form a portable representation of data. The data is encapsulated in key/value pairs and arranged in an orderly manner, with the values positioned at the end of the data items.
A key is a string of Unicode characters enclosed in double quotation marks, and the value is an integer or boolean. The data item must have a name and an associated key to be valid.
The names are written in curly brackets, and each item is separated by a comma (,). Arrays within a string are also separated by a comma, but if the value contains an element from an array, a nested comma must be used.
While XML has many advantages over JSON, there are still some disadvantages to the format. XML requires much more formatting, and the data can be difficult to understand.
On the other hand, JSON is a lightweight format and can be transferred easily between the client and server without consuming too much network bandwidth. It is a useful way to transport data in web applications, especially those using JavaScript as their main language.
Unlike XML, which can be hard to interpret, JSON is simple to read and easy to use. It is widely adopted and is available in every modern programming language, including JavaScript. It also supports flexible schema, making it easy to create complex object models for any application. It is also a preferred format for REST and GraphQL interfaces, which are built on top of JSON.
ISO-8601
The ISO-8601 date and time format is the international standard for formatting time and datetime values. The format uses UTC as the time scale, and it includes a time zone offset, which is a positive or negative number that represents the amount of time a time zone is east or west of the zero meridian.
The format is based on the Gregorian calendar, and it was developed by the International Organization for Standards (ISO). It can be used to track and monitor production schedules, and it’s easy to use on any computer system.
It’s a flexible and customizable format, so you can add or omit fields depending on your needs. It’s also a good choice for archiving logs and sharing them with others.
Another advantage of this format is that it’s a standard that is supported by all computer programs. It’s also easy to read and write.
However, there are some disadvantages. For example, it isn’t as flexible as some other formats and requires special software to process data. It can also cause problems when it’s used for storing sensitive information, like credit card numbers or bank account data.
Moreover, it’s not as simple to use as some other formats. You have to set up a table to store logs, and you have to create a DSN that the ODBC software will use to find the database.
Finally, it’s not as secure as other formats and it can be susceptible to human error. It’s also not as scalable as some other formats and can’t handle complex data structures.
If you’re looking for a more flexible log file format, consider using the W3C Extended log format. This format is a customizable ASCII format that limits the file size by only including the entries you want.
It is a popular choice for logging web pages, and it’s compatible with most operating systems and web servers. It also supports a number of fields, including the software that generated the log and the start and end dates for each entry.
Another common format is comma-separated values (CSV). It’s a classic format that has been around since the earliest computers, and it’s easier to read than some other types of data. It can also be nested, so you can nest different layers of information within the same log file.